Ligands for production of 1-hexene in chromium assisted ethylene oligomerization process

ABSTRACT

Catalyst compositions and processes for the oligomerization of ethylene to 1-hexene are described. The catalyst composition includes a triamino bisphospino (NPNPN) ligand system with specific phosphorous and nitrogen ligands. The terminal nitrogen atoms include linear alkyl hydrocarbons that differ in the number of carbon atoms by 3.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase application under 35 U.S.C. § 371of International Application No. PCT/IB2019/059672, filed Nov. 11, 2019,which claims the benefit of priority to U.S. Provisional PatentApplication No. 62/758,809, filed Nov. 12, 2018, the entire contents ofeach of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION A. Field of the Invention

The invention generally concerns a catalyst for the oligomerization ofethylene to 1-hexene. The catalyst includes a chromium (III) species anda ligand that promotes oligomerization selectivity of 1-hexene over1-octene.

B. Description of Related Art

Existing processes for the production of linear alpha olefins (LAOs),including comonomer-grade 1-butene, 1-hexene, and 1-octene, rely on theoligomerization of ethylene, and can lead to a mixture ofethylene-derived oligomers having a chain length of 4, 6, 8, and so on.Without being bound by theory, it is believed that this is due to achemical mechanism mainly governed by competing chain growth anddisplacement reaction steps, leading to a Schulz-Flory- orPoisson-product distribution. From a commercial standpoint this productdistribution poses a challenge for the full-range LAO producer as eachserved market segment can exhibit a different behavior in terms ofmarket size and growth, geography, fragmentation etc. It is, therefore,difficult for the LAO producer to adapt to the market requirements dueto part of the product spectrum might be in high demand in a giveneconomic context, while at the same time, other product fractions mightnot be marketable at all or only in a marginal niche. For example,certain grades of polyethylene materials call for modified physicalproperties such as modified tensile strength and crack resistance,requiring the presence of 1-hexene, but not other ethylene-derivedoligomers.

Oligomerization of ethylene usually proceeds in the presence of suitablecatalysts. Several of the existing ethylene oligomerization, i.e.,dimerization, trimerization or tetramerization, catalysts have one ormore disadvantages. These disadvantage can include: 1) low selectivityfor the desirable products; 1-hexene); 2) low selectivities for the LAOisomer within the C₆ cut (e.g., isomerization, branched olefin formationetc.); 3) wax formation (e.g., formation of heavy, long-chain (highcarbon-number) products); 4) polymer formation (polyethylene, includingbranched and/or cross-linked PE) that can lead to considerable LAOproduct yield loss as well as fouling of equipment; 5) poor turnoverrates/catalyst activity, resulting in increased cost per kg product; 6)high catalyst- or ligand cost; 7) complex, multi-step ligand synthesis,resulting in poor catalyst availability and high catalyst cost; 8)susceptibility of catalyst performance, both in terms of both activityand selectivity, to trace impurities (leading to, for example, catalystlosses/-poisoning); 9) difficult handling of catalyst components in atechnical/commercial environment (e.g., during catalyst complexsynthesis, pre-mixing, inertization, catalyst recovery, or ligandrecovery); 10) harsh reaction conditions, for example high temperaturesand pressure, resulting in a need for special equipment (increasedinvestment-, maintenance-, and energy costs); 11) highco-catalyst/activator cost or consumption; and/or 12) susceptibility tovarying co-catalyst qualities, which is often the case when largeramounts of relatively ill-defined compounds are used as activators(e.g., certain methylaluminoxane (MAO)-varieties).

Attempts to produce LAOs have been described. By way of example, U.S.Patent Application Publication No. 2017/0203288 to Al-Hazmi et al.describes the use of a catalyst composition that can include a chromiumcompound and an functionalized triamino, diphosphine (NPNPN) ligand ofthe formula (R¹) (R²)N—P(R³)—N(R⁴)—P(R⁵)—N(R⁶)(R⁷), wherein R¹, R², R³,R⁴, R⁵, R⁶, and R⁷ are each independently hydrogen, halogen, amino,tri-methylsilyl or C₁-C₂₀ hydrocarbyl, preferably straight-chain orbranched C₁-C₁₀ alkyl, phenyl, C₆-C₂₀ aryl or C₆-C₂₀ alkyl-substitutedphenyl. This catalyst suffers in that it produces about a greater than 8wt. % C₁₀₊, and about a 50:50 wt. % ratio of 1-hexene to 1-octene. Whenthe ratio increases to favor C₆ to C₈, the amount of C₁₀₊ alsoincreases, thus lowering the overall amount of desired product. In yetanother example, Peulecke (Dalton Transactions, 2016 45; 8869-8874)describes the production of mixtures of 1-hexene and 1-octene using aNPNPN ligand of the formula (R¹)(R²)N—P(Ph)—N(R³)—P(PH)—N(R⁴)(R⁵). Thiscatalyst system suffers in that greater than 11 wt. % C₁₀₊ is producedand the production of C₁₀₊ hydrocarbons increases as the yield of1-octene increases over the yield of 1-hexene.

There accordingly remains a need in the art for catalyst systems for theoligomerization of ethylene that can yield 1-hexene with highselectivity and purity.

SUMMARY OF THE INVENTION

A discovery has been made that provides a solution to at least some ofthe problems associated with the oligomerization of ethylene to1-hexene. The solution is premised on the use of a NPN(CH₃)PN ligandsystem having specific terminal amine alkyl substituents andphosphorous. Notably, the phosphorous substituents are limited tosubstituents that may be the same or different and selected from thegroup consisting of (i) C₃ to C₄ non-cyclic aliphatic groups, (ii) C₅ toC₇ aliphatic groups which may be cyclic or non-cyclic, linear orbranched, substituted or unsubstituted, and (iii) any combinationthereof; and preferably to cyclohexyl groups, and the terminal aminesinclude linear alkyl groups that differ in length by 3 carbon atoms. Asillustrated in a non-limiting way in the Examples, it was surprisingfound that limiting the substituents of the phosphorous atoms tosubstituents that may be the same or different and are selected from thegroup consisting of (i) C₃ to C₄ non-cyclic aliphatic groups, (ii) C₅ toC₇ aliphatic groups which may be cyclic or non-cyclic, linear orbranched, substituted or unsubstituted, and (iii) any combinationthereof; and preferably to cyclohexyl groups, and the length of thehydrocarbon chain on the terminal nitrogen atoms produces at least 80wt. % 1-C₆ hydrocarbon at a selectivity of greater than 99%, 1-hexeneand less than 3 wt. % solvent insoluble material (e.g., C₁₀₊) material.

In one aspect of the present invention, catalyst compositions for theoligomerization of ethylene to 1-hexene are described. A catalystcomposition can include a chromium (III) species and a ligand having theformula of:

where R¹ and R² are the same or different and are selected from thegroup consisting of (i) C₃ to C₄ non-cyclic aliphatic groups, (ii) C₅ toC₇ aliphatic groups which may be cyclic or non-cyclic, linear orbranched, substituted or unsubstituted, and (iii) any combinationthereof; and, wherein n is 0 or 1, and m=n+3. In some embodiments, R¹and R² are each independently a cyclohexyl group or an alkyl substitutedcyclohexyl group, preferably both are cyclohexyl groups. In oneinstance, n is 0 and the catalyst is(CH₃)(n-C₄H₉)NP(C₆H₁₁)N(CH₃)NP(C₆H₁₁)N(CH₃)(n-C₄H₉) represented by thefollowing structure:

In another instance, n is 1 and the catalyst is(CH₃CH₂)(n-C₅H₁₁)NP(C₆H₁₁)N(CH₃)NP(C₆H₁₁)N(CH₂CH₃)(n-C₅H₁₁) representedby the following structure:

The catalyst composition can also include an activator or co-catalyst(e.g., methylaluminoxane compounds, preferably, methyl iso-butylaluminum oxide compound). Chromium (III) species can include anyinorganic or organic chromium compound where chromium has a valance of+3. Non-limiting examples of chromium (III) species include chromium(III) acetylacetonate, Cr(2,2,6,6,-tetramethyl-3,5-heptadionate)₃,chromium(III)2-ethylhexanoate, chromium trichloridetris-tetrahydrofuran; chromium (III) octanoate; chromium (III)naphthenate, or any combination thereof.

Processes for producing 1-hexene using the catalyst composition of thepresent invention are also described. A process to produce 1-hexene caninclude contacting a reactant stream comprising an olefin source with asolution comprising the catalyst composition of the present invention toproduce an oligomer composition that includes 1-hexene. The catalystcomposition can also include a solvent (e.g., a saturated hydrocarbon,preferably n-hepane, an aromatic hydrocarbon, preferably toluene,methylcyclohexane, or a mixture thereof). The contacting step caninclude a temperature of 15° C. to 100° C., preferably 40° C. to 70° C.and/or a pressure of at least 2 MPa or 2 to 20 MPa, preferably 2 to 7MPa. During the process, solvent insoluble material (e.g., polymericmaterial) can be produced at less than 2 wt. %, preferably less than 5wt. % or more preferably less than 0.5 wt. %, or not at all). In someinstances, the catalyst composition can include

a chromium (III) species, and an activator or a co-catalyst. In otherinstances, the catalyst composition can include

the chromium (III) species, and the activator or co-catalyst. In someembodiments, the product stream can include 1-octene. In suchembodiments, the reaction selectivity for 1-hexene can be greater than80%, and/or a weight ratio of 1-octene to 1-hexene can be less than0.25.

Other embodiments of the invention are discussed throughout thisapplication. Any embodiment discussed with respect to one aspect of theinvention applies to other aspects of the invention as well and viceversa. Each embodiment described herein is understood to be embodimentsof the invention that are applicable to other aspects of the invention.It is contemplated that any embodiment discussed herein can beimplemented with respect to any method or composition of the invention,and vice versa. Furthermore, compositions of the invention can be usedto achieve methods of the invention.

The following includes definitions of various terms and phrases usedthroughout this specification.

The term “aliphatic” means an organic functional group or compoundcontaining carbon and hydrogen joined together in straight chains,branched chains, or non-aromatic rings.

The term “alkyl group” refers to a linear or a branched saturatedhydrocarbon. Non-limiting examples of alkyl groups include methyl,ethyl, propyl, butyl, pentyl, etc.

An “aryl” group or an “aromatic” group is a substituted or substituted,mono- or polycyclic hydrocarbon with alternating single and double bondswithin each ring structure. Non-limiting examples of aryl groupsubstituents include alkyl, substituted alkyl groups, linear or branchedalkyl groups, linear or branched unsaturated hydrocarbons, halogen,hydroxyl, alkoxy, haloalkyl, haloalkoxy, carboxylic acid, ester, amine,nitro, amide, nitrile, acyl, alkyl silane, thiol and thioethersubstituents. Non-limiting examples of alkyl groups include linear andbranched C₁ to C₅ hydrocarbons. Non-limiting examples of unsaturatedhydrocarbons include C₂ to C₅ hydrocarbons containing at least onedouble bond (e.g., vinyl). The aryl or alkyl group can be substitutedwith the halogen, hydroxyl, alkoxy, haloalkyl, haloalkoxy, carboxylicacid, ester, ether, amine, nitro (—NO₂), amide, nitrile (—CN), acyl,alkyl silane, thiol and thioether substituents. Non-limiting examples ofhalogens include chloro (—Cl), bromo (—Br), or fluoro (—F) substituents.Non-limiting examples of haloalkyl substituents include —CX₃, —CH₂X,—CH₂CH₂X, —CHXCH₂X, —CX₂CHX₂, —CX₂CX₂ where X is F, Cl, Br orcombinations thereof. Non-limiting examples, of amine substituentsinclude —NH₂, —CH₂NH₂, —CHCH₂NH₂, —C(NH₂)CH₃. Non-limiting examples ofalkoxy include —OCH₃, —OCH₂CH₃, and the like. Non-limiting examples, ofalkyl silane substituents include —Si(CH₃)₃, —Si(CH₂CH₃)₃, and the like.Non-limiting examples of polycyclic groups include ring systems thatinclude 2 or more conjugated rings (e.g., fused aromatic rings) andsubstituted conjugated rings such as —C₁₀H₇ and substituted ten carbonconjugated ring systems.

A “C₃ to C₄ non-cyclic aliphatic group” means a non-cyclic hydrocarbongroup containing 3 or 4 carbon atoms, with non-limiting examplesincluding iso-propyl and tert-butyl. A “C₅ to C₇ group” is a hydrocarbongroup containing 6, 7, or 8 carbon atoms, with non-limiting examplesincluding pentyl, hexyl, heptyl, and cyclohexyl. A “C₅ to C₇ substitutedor unsubstituted cycloalkane group” means a substituted orunsubstituted, cyclic hydrocarbon group containing 6, 7, or 8 carbonatoms, with non-limiting examples including cyclopentyl, cyclohexyl, andcycloheptyl. When fully saturated with hydrogen and having the formulaC₅H₉, C₆H₁₁, C₇H₁₃, it is a C₅ to C₇ unsubstituted cycloalkane group.When at least one of the hydrogen atoms is replaced by another atom orfunctional group, it is a C₅ to C₇ substituted cycloalkane group.

A “cyclohexyl” group is a substituted or unsubstituted, cyclichydrocarbon group containing 6 carbon atoms. When fully saturated withhydrogen and having the formula C₆H₁₁, the cyclohexyl group is anunsubstituted cyclohexyl group. When at least one of the hydrogen atomsis replaced by another atom or functional group, the cyclohexyl group isan substituted cyclohexyl group.

The phrase “solvent insoluble” refers to polymer material with themolecular weight 500 g/mol and above (30+ carbon atoms) and is presentin amounts of less than <2 wt. %, preferably <1 wt. %, more preferably<0.5 wt. % as determined gravimetrically.

The terms “about” or “approximately” are defined as being close to asunderstood by one of ordinary skill in the art. In one non-limitingembodiment, the terms are defined to be within 10%, preferably within5%, more preferably within 1%, and most preferably within 0.5%.

The terms “wt. %”, “vol. %”, or “mol. %” refers to a weight percentageof a component, a volume percentage of a component, or molar percentageof a component, respectively, based on the total weight, the totalvolume of material, or total moles, that includes the component. In anon-limiting example, 10 grams of component in 100 grams of the materialis 10 wt. % of component.

The term “substantially” and its variations are defined to includeranges within 10%, within 5%, within 1%, or within 0.5%.

The terms “inhibiting” or “reducing” or “preventing” or “avoiding” orany variation of these terms, when used in the claims and/or thespecification includes any measurable decrease or complete inhibition toachieve a desired result.

The term “effective,” as that term is used in the specification and/orclaims, means adequate to accomplish a desired, expected, or intendedresult.

The use of the words “a” or “an” when used in conjunction with any ofthe terms “comprising,” “including,” “containing,” or “having” in theclaims, or the specification, may mean “one,” but it is also consistentwith the meaning of “one or more,” “at least one,” and “one or more thanone.”

The words “comprising” (and any form of comprising, such as “comprise”and “comprises”), “having” (and any form of having, such as “have” and“has”), “including” (and any form of including, such as “includes” and“include”) or “containing” (and any form of containing, such as“contains” and “contain”) are inclusive or open-ended and do not excludeadditional, unrecited elements or method steps.

The catalyst compositions of the present invention can “comprise,”“consist essentially of,” or “consist of” particular ingredients,components, compositions, etc. disclosed throughout the specification.With respect to the transitional phrase “consisting essentially of,” inone non-limiting aspect, a basic and novel characteristic of thecatalyst compositions of the present invention are their abilities tocatalyze the oligomerization of ethylene to 1-octene in greater than 80%selectivity with the production of minimal amounts of solvent insolublematerial (e.g., <3 wt. %).

In the context of the present invention at least twenty embodiments arenow described. Embodiment 1 is a catalyst composition for theoligomerization of ethylene to 1-hexene. The catalyst compositioncontains a chromium (III) species; and a ligand having the formula of:

where R¹ and R² are the same or different and are selected from thegroup consisting of (i) C₃ to C₄ non-cyclic aliphatic groups, (ii) C₅ toC₇ aliphatic groups which may be cyclic or non-cyclic, linear orbranched, substituted or unsubstituted, and (iii) any combinationthereof; and, wherein n is 0 or 1, and m=n+3. Embodiment 2 is thecatalyst composition of embodiment 1, wherein R¹ and R² are eachindependently a cyclic hydrocarbon group, a substituted cyclichydrocarbon group, a linear hydrocarbon group or a branched hydrocarbongroup having 1 to 10 carbon atoms. Embodiment 3 is the catalystcomposition of embodiment 2, wherein R1 and R2 are each a cyclohexylgroup. Embodiment 4 is the catalyst composition of embodiment 3, whereinn is 0, and the catalyst has the structure of:

Embodiment 5 is the catalyst composition of embodiment 3, wherein n is 1and the catalyst has the structure of

Embodiment 6 is the catalyst composition of any one of embodiments 1 to5, wherein the composition further contains an activator or co-catalyst.Embodiment 7 is the catalyst composition of embodiment 6, wherein theactivator or co-catalyst is a methylaluminoxane compound. Embodiment 8is the catalyst composition of embodiment 6, wherein the activator orco-catalyst is a methyl iso-butyl aluminum oxide compound. Embodiment 9is the catalyst composition of embodiment 1, wherein the chromium (III)species is selected from the group consisting of chromium (III)acetylacetonate, Cr(2,2,6,6,-tetramethyl-3,5-heptadionate)₃,chromium(III)2-ethylhexanoate, chromium trichloridetris-tetrahydrofuran; (benzene)tricarbonyl chromium; chromium (III)octanoate and chromium (III) naphthenate. Embodiment 10 is the catalystcomposition of embodiment 1, wherein one or both of R¹ and R² areselected from the group consisting of iso-propyl and tert-butyl.Embodiment 11 a process to produce 1-hexene from ethylene, the processincluding the steps of contacting a reactant stream containing an olefinsource with a solution comprising the catalyst composition of any one ofembodiments 1 to 9 to produce a oligomer composition comprising1-hexene. Embodiment 12 is the process of embodiment 11, wherein thesolution includes a solvent. Embodiment 13 is the process of embodiment12, wherein the solvent is a saturated hydrocarbon. Embodiment 14 is theprocess of embodiment 13, wherein the solvent is n-hexane,methylcyclohexane, or a mixture thereof. Embodiment 15 is the process ofany one of embodiments 11 to 14, wherein the product stream furtherincludes 1-octene and a selectivity for 1-hexene is greater than 99%,and a weight ratio of 1-octene to 1-hexene is less than 0.15. Embodiment16 is the process of embodiment 15, wherein the catalyst compositioncontains

Embodiment 17 is the process of any one of embodiment 15, furtherincluding the chromium (III) species, the activator or co-catalyst.Embodiment 18 is the process of any one of embodiment 11 to 17, whereinthe catalyst composition contains the chromium (III) species, theactivator or co-catalyst and

Embodiment 19 is the process of any one of embodiments 11 to 18, whereinthe contacting includes a temperature of 15° C. to 100° C., preferably40° C. to 70° C. Embodiment 20 is the process of any one of embodiments11 to 19, wherein the contacting is conducted at a pressure of at least2 MPa or 2 to 20 MPa, preferably 2 to 7 MPa.

Other objects, features and advantages of the present invention willbecome apparent from the following figures, detailed description, andexamples. It should be understood, however, that the figures, detaileddescription, and examples, while indicating specific embodiments of theinvention, are given by way of illustration only and are not meant to belimiting. Additionally, it is contemplated that changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description. Infurther embodiments, features from specific embodiments may be combinedwith features from other embodiments. For example, features from oneembodiment may be combined with features from any of the otherembodiments. In further embodiments, additional features may be added tothe specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention may become apparent to those skilledin the art with the benefit of the following detailed description andupon reference to the accompanying drawings.

FIG. 1 is an illustration of a schematic of a system to produce 1-hexenefrom the oligomerization of ethylene.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings. The drawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

A discovery has been made that provides a way to produce 1-hexene inacceptable yields, in high selectivity, and without making significantamounts of solvent insoluble material from the oligomerization ofethylene. The discovery is premised on using a NPNPN ligand system.Notably, and as illustrated in a non-limiting manner in the examples, anoligomerization product stream can include at least 80 wt. % C₆hydrocarbon, less than 10 wt. % C₈ hydrocarbon, and less than 3 wt. %solvent insoluble material (e.g., polymeric materials). This is contrastto the ligands of the prior art, which produce more than 3 wt. %polymeric materials. The critical parameters include the choice ofphosphorous substituents and nitrogen substituents. The phosphoroussubstituents include an aromatic group or an alkyl substituted aromaticgroup, the middle nitrogen substituent includes a methyl substituent,and the terminal nitrogen substituents include different linear alkylhydrocarbons groups that differ in the number of carbon atoms by 3. Thiscombination of substituents provides an elegant and simple ligand systemfor the production of 1-hexene in high purity and selectivity above 80wt. %.

These and other non-limiting aspects of the present invention arediscussed in further detail in the following sections.

A. Catalyst Composition

The catalyst composition can include the ligands of the presentinvention, a chromium (III) species, and an activator or co-catalyst.The ligands of the present invention can be prepared as describedthroughout the specification and in the Examples. The catalystcomposition can be provided as a solution in an aliphatic or aromatichydrocarbon solvent. Aliphatic hydrocarbon solvents can include hexane,methylcyclohexane, cyclohexane, n-heptane and the like.

The ligands of the present invention can be represented by the followingformula:

where R¹ and R² selected from the group consisting of (i) C₃ to C₄non-cyclic aliphatic groups, (ii) C₅ to C₇ aliphatic groups which may beeach be cyclic or non-cyclic, linear or branched, substituted orunsubstituted, and (iii) any combination thereof, and wherein n is 0 or1, and m=n+3. The C₅ to C₇ aliphatic groups can substituted orunsubstituted cycloalkane groups include cyclopentyl, cyclohexyl,cycloheptyl, substituted cyclopentyl, substituted cyclohexyl, andsubstituted cycloheptyl. The C₃ to C₄ non-cyclic aliphatic groups can beiso-propyl and tert-butyl. The ligands can be(CH₃)(n-C₄H₉)NP(R¹)N(CH₃)NP(R²)N(CH₃)(n-C₄H₉) and(CH₃CH₂)(n-C₅H₁₁)NP(R¹)N(CH₃)NP(R²)N(CH₂CH₃)(n-C₅H₁₁)(CH₃)(n-C₄H₉)NP(C₆H₁₁)N(CH₃)NP(C₆H₁₁)N(CH₃)(n-C₄H₉) and(CH₃CH₂)(n-C₅H₁₁)NP(C₆H₁₁)N(CH₃)NP(C₆H₁₁)N(CH₂CH₃)(n-C₅H₁₁). Thestructure of the ligands can be illustrated as follows:

where R₁ and R₂ represent alkyl groups such as methyl, ethyl, propyl,isopropyl, butyl, tert-butyl, and pentyl, and the like.

The NPNPN ligand system can be made by synthetic approaches known tothose skilled in the art. In some embodiments, ligand (1) is accessibleby reaction pathways as shown in Scheme I.

where R¹ and R² are defined above, and R₃ is methyl or ethyl and R₄ isbutyl when R₃ is methyl and pentyl when R₃ is ethyl.

The chromium species can be an organic salt, an inorganic salt, acoordination complex, or an organometallic complex of Cr(III). In anembodiment, the chromium species is an organometallic Cr(III) species.Non-limiting examples of the chromium species includeCr(III)acetylacetonate, Cr(III)octanoate, CrCl₃ (tetrahydrofuran)₃,Cr(III)-2-ethylhexanoate, Cr(III)chloride, or any combination thereof.The molar ligand/Cr ratio can be from about 0.5 to 50, about 0.5 to 5,about 0.8 to about 2.0, about 1.0 to 5.0, or preferably from about 1.0to about 1.5.

The activator (also known in the art as a co-catalyst) can be analuminum compound. Non-limiting examples of aluminum compounds includetrimethylaluminum, triethylaluminum, triisopropylaluminum,triisobutylaluminum, diethylaluminum chloride, ethylaluminumsesquichloride, ethylaluminum dichloride, methylaluminoxane, or amixture thereof. In some embodiments, the activator can be a modifiedmethylaluminoxane, more preferably MMAO-3A (CAS No. 146905-79-5), whichis a modified methylaluminoxane, type 3A, available from Akzo Nobel intoluene solution containing 7% aluminum, which corresponds to an MMAO-3Aconcentration of about 18%. The molar Al/Cr ratio can be from about 1 toabout 1000, about 10 to about 1000, about 1 to 500, about 10 to 500,about 10 to about 300, about 20 to about 300, or preferably from 50 toabout 300.

The catalyst composition can further include a solvent. Non-limitingexamples of solvents are straight-chain and cyclic aliphatichydrocarbons, straight-chain olefins, ethers, aromatic hydrocarbons, andthe like. A combination comprising at least one of the foregoingsolvents can be used. Preferably, the solvent is n-heptane, toluene, ormethylcyclohexane or any mixture thereof.

The concentration of the chromium compound in the solvent vary dependingon the particular compound used and the desired reaction rate. In someembodiments, the concentration of the chromium compound is from about0.01 to about 100 millimole per liter (mmol/l), about 0.01 to about 10mmol/l, about 0.01 to about 1 mmol/l, about 0.1 to about 100 mmol/l,about 0.1 to about 10 mmol/l, about 0.1 to about 10 mmol/l, about 1 toabout 10 mmol/l, and about 1 to about 100 mmol/l. Preferably, theconcentration of the chromium compound is from about 0.1 to about 1.0mmol/l.

In some embodiments, the catalyst composition includesCr(III)acetylacetonate as the chromium compound,Et(n-pentyl)N—P(cyclohexyl)-N(Me)-P(cyclohexyl)-N(n-pentyl)Et as theNPNPN ligand, and MMAO-3A as the activator. In another embodiment, thecatalyst composition includes Cr(III)acetylacetonate as the chromiumcompound, Me(n-butyl)N—P(cyclohexyl)-N(Me)-P(cyclohexyl)-N(n-butyl)Me asthe NPNPN ligand, and MMAO-3A as the activator.

B. System for Oligomerization of Olefins to 1-Hexene

The catalyst composition of the present invention can be used in aprocess for the oligomerization of ethylene to 1-hexene. In anembodiment, the process encompasses contacting ethylene with thecatalyst composition under ethylene oligomerization conditions effectiveto produce 1-hexene. Those skilled in the art will understand thatoligomerization of ethylene to produce 1-hexene can be by trimerizationof ethylene.

FIG. 1 depicts a schematic for a system to produce 1-hexene. The system100 can include an inlet 102 for a reactant feed that includes ethylene,a reaction zone 104 that is configured to be in fluid communication withthe inlet, and an outlet 106 configured to be in fluid communicationwith the reaction zone 104 and configured to remove a product streamfrom the reaction zone. The reactant zone 104 can include the catalystcomposition of the present invention. The ethylene reactant feed canenter the reaction zone 104 via the inlet 102. In some embodiments, theethylene reactant feed can be used to maintain a pressure in thereaction zone 104. In some embodiments, the reactant feed streamincludes inert gas (e.g., nitrogen or argon). After a sufficient amountof time, the product stream can be removed from the reaction zone 104via product outlet 106. The product stream can be sent to otherprocessing units, stored, and/or transported.

System 100 can include one or more heating and/or cooling devices (e.g.,insulation, electrical heaters, jacketed heat exchangers in the wall) orcontrollers (e.g., computers, flow valves, automated values, etc.) thatcan be used control the reaction temperature and pressure of thereaction mixture. While only one reactor is shown, it should beunderstood that multiple reactors can be housed in one unit or aplurality of reactors housed in one heat transfer unit.

As discussed above, the process and catalyst composition of the presentinvention allows for the production of 1-hexene with high selectivitywith the LAO product distribution being limited to 1-hexene and1-octene. High selectivity for 1-hexene is an advantageous featureinasmuch as it leads to higher product purity, thereby circumventing theneed for additional purification steps in the separation train. Furtheradvantageous features of the catalyst composition and process includesuppression of ethylene polymerization leading to undesirable polymerformation, milder reaction conditions and, as a result, lower capitalcosts for equipment as well as operational and energy costs.Additionally, a relatively simple, straight-forward process design ispossible. The selectivity for 1-hexene is greater than 80 wt. %, 85 wt.%, 90 wt. %, 95 wt. %, or about 100 wt. %, or any range or valuetherebetween. The purity for 1-hexene can be at least about 99%, or99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, or 99.9%. Apurity of at least 99.1% is preferred. In an embodiment, when 1-octeneis produced, the weight ratio of 1-octene to 1-hexene can be less than0.3, or 0 to 0.3, or 0.1, 0.15, 0.2, 0.25 or 0.3 or any range or valuethere between.

EXAMPLES

The present invention will be described in greater detail by way ofspecific examples. The following examples are offered for illustrativepurposes only, and are not intended to limit the invention in anymanner. Those of skill in the art will readily recognize a variety ofnoncritical parameters which can be changed or modified to yieldessentially the same results.

Example 1 Synthesis of Ligands 2 and 3

Route A, General Procedure (See, Scheme 1). All manipulations werecarried out under inert atmosphere. Bis(chlorophosphino)amineC₆H₁₁P(Cl)N(CH₃)P(Cl)C₆H₁₁ (4.60 g, 14 mmol) was dissolved in 20 mL ofanhydrous toluene. Appropriate secondary amine (29.4 mmol) and NEt₃ (35mmol) was mixed with 30 mL of anhydrous toluene and cooled down to −10°C. Toluene solution of bis(chlorophosphino)amine was added dropwise tothe reaction mixture under inert atmosphere with vigorous stirring.Addition of the reagent resulted in precipitation of white gel-likematerial. With continuous stirring, solution was left to warm up to 25°C. for 3 hours, then heated to 75° C. and stirred at that temperaturefor additional 12 hrs. After evaporation of all volatile compounds undervacuum, the residue was taken up in anhydrous hot n-heptane andinsoluble material was separated by filtration. Evaporation of thesolvent led to pale yellow oil. Purity of the product was verified using¹H, ¹³C and ³¹P NMR. If desired, the products can be recrystallized fromn-hexane, cyclohexane, n-heptane or n-pentane to increase the purity.

Route B, General Procedure (See, Scheme 1). All manipulations werecarried out under inert atmosphere. The appropriate secondary amine (10mmol) was dissolved in 20 mL of anhydrous n-heptane, cooled down to −10°C. and treated with 5% mol. excess of n-BuLi in n-hexane. The solutionwas then stirred for 3 hrs letting the temperature raise to 25° C.,forming white precipitate. Solid was separated from solution, washedwith n-hexane and transferred to the flask with 30 mL of anhydrous Et₂O.Resulted suspension was cooled down to −10° C. and solution ofbis(chlorophosphino) amine C₆H₁₁P(Cl)N(CH₃)P(Cl)C₆H₁₁ (1.61 g, 4.9 mmol)in 30 mL of anhydrous Et₂O was added dropwise to the reaction mixturewith vigorous stirring. After the addition, reaction mixture wascontinuously stirred for 12 hours letting it warm up to 25° C. Duringthe course of the reaction, white solid was formed. Insoluble materialwas separated by filtration, washed with Et₂O and discarded. Solutionand washing liquids were combined and solvent was removed in vacuum,producing pale yellow viscous oil. Purity of the product was verifiedusing ¹H, ¹³C and ³¹P NMR. If desired, the products can berecrystallized from n-hexane, cyclohexane, n-heptane or n-pentane toincrease the purity.

Precursor (C₆H₁₁)P(Cl)N(Me)P(Cl)(C₆H₁₁) was prepared by the procedure ofJefferson et al. (J. Chem. Soc. Dalton Trans. 1973, 1414-1419).

Example 2 Catalyst Composition Preparation and Oligomerization ofEthylene

The reactor, equipped with dip tube, thermowell, mechanical paddlestirrer, cooling coil, control units for temperature, pressure andstirrer speed (all hooked up to a data acquisition system) was preparedfor the catalytic run by heating to 130° C. in under vacuum for 4 hoursand cooled down by venting with dry nitrogen stream to 30° C. Anisobaric ethylene supply was maintained by gas dosing control unitconnected to data acquisition system. Ethylene consumption was monitoredvia pressure loss in the feeding cylinder over time by means of acomputerized data acquisition system.

Suitable amounts of the stock toluene solutions of the ligands andCr(III)acetylacetonate as chromium precursor, at a ligand to Cr ratio of1.20, were measured and charged to a Schlenk tube under inertatmosphere. A volume of 30 mL anhydrous n-heptane was introduced instainless steel pressure reactor and warmed up to desired reactiontemperature. After temperature of the reactor become stable, reactor waspressurized to 30 bar of ethylene and left for 30 min with continuousmechanical stirring. After that time, pressure was reduced to 0.2 barand appropriate amount of 0.3M stock solution of MMAO-3A in anhydrousn-heptane was introduced in the reactor through the charging port,providing Al to Cr ratio of 300. Stirring was continued for 10 min.Following that, mixture of Cr and ligand solutions was introduced intothe reactor through the charging port.

Immediately after introduction of the catalyst in the reactor, pressurewas increased to 30 bar. Standard reaction conditions are: pressure ofethylene of 30 bar, T=45° C., stirrer speed of 450 RPM. After 1 hourcatalytic run, ethylene supply was cut and reactor temperature loweredto 5° C. Ethylene from the reactor was vented to the pressure of 0.2bar. The reaction was quenched with 0.3M HCl/iso-Propanol mixture. Itshould be noted that it is also possible to quench the reaction withdifferent agents, such as Decan-1-ol, 2-EHA, 20% wt. NaOH in water.Liquid products were analyzed using gas chromatography with a knownamount of toluene as internal standard. Any insoluble by-products, i.e.,waxes, polyethylene, were filtered, dried, and weighed. Table 1 showsthe results of ligand

S12 catalyst includes the ligand is that shown as structure (2) above(having two methyl and two n-butyl substituents).

TABLE 1 Activity Solvent (kg/ % wt. C6 % wt. C8 Insoluble Catalystg_(Cr) * h) (1-hexene, %) (1-octene, %) % wt. S12 (Run 1) 56.50 85.62(99.45)  9.69 (95.80) 2.28 S12 (Run 2) 169.00 87.99 (99.92)  5.71(99.95) 0.53 S6 179.15 21.55 (79.20) 76.86 (99.41) 0.32 (Comparative;Structure (7)) S1 95.45 40.10 (76.78) 58.11 (96.13) 1.09 (Comparative;Structure (6))

Table 1 summarizes the results of ethylene oligomerization experimentalruns performed under these standard conditions and using catalystsystems prepared with the catalyst S12 with ligand (2) and a comparativecatalysts. The Table shows the respective selectivities for C6, C8, andsolvent insolubles in wt. % in the liquid phase. Numbers in parenthesesdenote the selectivities of the respective linear alpha-olefin in theoverall C6/C8 fraction. These LAO purities are generally advantageouslyhigh. The comparative catalyst differs from catalyst S12 in thatcatalyst S12 includes the ligands shown in Formula (2) in thisspecification, while the comparative catalysts include the ligands shownin Formula (6) and (7) have two phenyl groups replacing the twocyclohexyl groups in Formula (2). Two runs are shown for S12 catalyst.It was observed that a second consecutive run typically demonstratesbetter performance than the initial run. Although not wanting to bebound by theory, it is suspected that this quite typical behavior islikely attributable to the reactor being dried and cleaned during thefirst run. Notwithstanding the improvement from the first and secondrun, the data clearly demonstrates the different behavior in comparisonto S12 and S6 species, which have aromatic groups on the two phosphorusatoms.

Although embodiments of the present application and their advantageshave been described in detail, it should be understood that variouschanges, substitutions and alterations can be made herein withoutdeparting from the spirit and scope of the embodiments as defined by theappended claims. Moreover, the scope of the present application is notintended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the above disclosure, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein can be utilized. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

The invention claimed is:
 1. A catalyst composition for theoligomerization of ethylene to 1-hexene, the catalyst compositioncomprising: a chromium (III) species; and a ligand having the formulaof:

where R¹ and R² are the same or different and are selected from thegroup consisting of (i) C₃ to C₄ non-cyclic aliphatic groups, (ii) C₅ toC₇ aliphatic groups which may be cyclic or non-cyclic, linear orbranched, substituted or unsubstituted, and (iii) any combinationthereof; and, wherein n is 0 or 1, and m=n+3.
 2. The catalystcomposition of claim 1, wherein R¹ and R² are each independently acyclic hydrocarbon group, a substituted cyclic hydrocarbon group, alinear hydrocarbon group or a branched hydrocarbon group having 1 to 10carbon atoms.
 3. The catalyst composition of claim 2, wherein R¹ and R²are each a cyclohexyl group.
 4. The catalyst composition of claim 3,wherein n is 0, and the ligand has the structure of:


5. The catalyst composition of claim 3, wherein n is land the ligand hasthe structure of:


6. The catalyst composition of claim 1, wherein the composition furthercomprises an activator or co-catalyst.
 7. The catalyst composition ofclaim 6, wherein the activator or co-catalyst is a methylaluminoxanecompound.
 8. The catalyst composition of claim 6, wherein the activatoror co-catalyst is a methyl iso-butyl aluminum oxide compound.
 9. Thecatalyst composition of claim 1, wherein the chromium (III) species isselected from the group consisting of chromium (III) acetylacetonate,Cr(2,2,6,6,-tetramethyl-3,5-heptadionate)₃,chromium(III)2-ethylhexanoate, chromium trichloride;tris-tetrahydrofuran, (benzene)tricarbonyl chromium, chromium (III)octanoate and chromium (III) naphthenate.
 10. The catalyst compositionof claim 1, wherein one or both of R¹ and R² are selected from the groupconsisting of iso-propyl and tert-butyl.
 11. A process to produce1-hexene from ethylene, the process comprising contacting a reactantstream comprising an olefin source with a solution comprising thecatalyst composition of claim 1 to produce a oligomer compositioncomprising 1-hexene.
 12. The process of claim 11, wherein the solutioncomprises a solvent.
 13. The process of claim 12, wherein the solvent isa saturated hydrocarbon.
 14. The process of claim 13, wherein thesolvent is n-hexane, methylcyclohexane, or a mixture thereof.
 15. Theprocess of claim 11, wherein the oligomer product further comprises1-octene and a selectivity for 1-hexene is greater than 99%, and aweight ratio of 1-octene to 1-hexene is less than 0.15.
 16. The processof claim 15, wherein the ligand comprises:


17. The process of claim 15, wherein the solution further comprises anactivator or co-catalyst.
 18. The process of claim 11, wherein thecatalyst composition comprises the chromium (III) species, an activatoror co-catalyst and the ligand has the structure of:


19. The process of claim 11, wherein the contacting comprises atemperature of 15° C. to 100° C.
 20. The process of claim 11, whereinthe contacting comprises a pressure of at least 2 MPa or 2 to 20 MPa.